Media Oriented Systems Transport (MOST) is a network configuration that employs a ring topology. MOST was developed for use within automobiles and is intended to provide a robust networking solution able to withstand the harsh operating environment that is characteristic of automobiles. MOST enables the seamless transport of digital audio, video, packet-based data, and control information among multiple nodes in the network.
The MOST specification, for example version 2.4 as promulgated by the Most Cooperation of Karlsruhe, Germany, defines all seven layers of the ISO/OSI Reference Model for data communication. Within a MOST network, a Timing Master node (master) continuously feeds frames of data into the network or acts as a gate for data. The master generates frames of data at a rate that supports playback of CD quality audio, DVD encoded video, and/or multimedia content within the MOST network. Other nodes within the MOST network are timing slave nodes that are synchronized by a preamble, which is located within a header portion of the frames.
Within a MOST network, data is organized into frames of 64 bytes. The frames are organized into blocks of 16 frames. The blocks are organized into super blocks of 64 blocks. Each frame is subdivided into different segments. For example, each frame will include, among other data, a header, one or more control bits, a synchronous field, and an asynchronous field. The asynchronous field will typically include packet data that is to be distributed throughout the network. Large packets of data, however, may not fit within the asynchronous field of a single frame. In such cases, it becomes necessary to divide the packet into several smaller sub-packets to be sent within multiple frames.
For example, consider the case where a packet is subdivided into five smaller sub-packets and each sub-packet is inserted into the asynchronous field within one of five different frames. These five frames may be consecutively transmitted through the MOST network. A receiving node within the MOST network can assemble the packet by extracting the sub-packets from each of the five frames.
Nodes transmit information within the MOST network by obtaining the right to insert data into the asynchronous field of one or more frames. In this regard, the frame and/or asynchronous field may be referred to as a “shared channel” in that the asynchronous field can be made available to any node within the MOST network. For a node to insert data into the asynchronous field, the shared channel first must become available or free. From time to time, whether due to data corruption or malfunction of a node, the asynchronous field does not become available, e.g., is not released. The result is as if one node is monopolizing the shared channel. This creates a deadlock state where no other node within the MOST network is able to take control of the shared channel and transmit data.